Shielded electrode tube



April 14, 1936. R. M. HElNTZ 2,037,231

SHIELDED ELECTRODE TUBE Original Filed Sept. 6, 1933 INVENTOR RALPH M HE/NTZ.

Patented Apr. 14, 1936 UNETED STATES PATENT OFFICE SHIELDED ELECTRODE TUBE Original application September 6, 1933, Serial No.

688,328. Divided and this application Decemher 17, 1934, Serial No. 757,752

1 Claim.

My invention relates to a thermionic tube, and more particularly to a tube in which the anode and cathode are separated by an electrostatic shield which also acts as a control electrode.

This application is a division of my prior application, Serial No. 688,328, filed September 6, 1933.

Among the objects of my invention are: to provide a thermionic tube capable of oscillation at ultra high frequencies; to provide a thermionic tube in which a control electrode acts as an electrostatic shield between anode and cathode; to provide a tube having a control electrode extend ing to the side walls of an envelope and adapted to cooperate with an external shield to regulate the effective capacity between anode and cathode; to provide a thermionic tube having a control electrode adapted to operate at ground potential; and to provide a thermionic tube wherein the anode and cathode and their associated circuits may be substantially shielded from each other.

Other objects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claim.

Referring to the drawing which illustrates sev- 30 eral embodiments of my invention, all somewhat diagrammatically represented for the sake of clearness:

Figure l is a longitudinal sectional view of a thermionic tubev embodying my invention. Figure 2 is a cross sectional View taken as indicated by the line 2-2 in Figure 1.

Figure 3 is a longitudinal sectional View of an embodiment wherein the envelope is distorted so that the periphery of the inner control electrode 40 may overlap an external shield.

Figure 4 is a circuit diagram, reduced to lowest terms, of the tube of my invention connected as an oscillation generator.

In the generation and amplification of ultra high frequency radio waves, interelectrode capacities, especially those capacities which occur between electrodes of fluctuating potentials, become. so important as to require, in many cases, special neutralizing expedients. Such expedients 50 invariably produce loss and reduce efliciency of conversion. In addition, at wave lengths around three meters and below, the usual type of threeelectrode tube is practically useless for the generation of any appreciable amount of oscillating 55 current.

Attempts have heretofore been made to separate the fluctuating potentials by using opposed grid and anode, and inserting the filament between them. The filamentary cathode being grounded, acts as a partial shield between the "5 other electrodes. Such a construction, while. an improvement over ordinary types of tubes, is subject to the disadvantage of having a low amplification factor, and. as the control is electrostatic the shielding effect of the cathode can only be increased at the expense of loss of control.

I have, however, been able to completely shield the fluctuating electrodes in a thermionic tube.

In broad terms, my invention comprises shaping the grid into an electrostatic shield between anode and. cathode. I prefer to have the grid material extend to the envelope walls along all radii where it may cooperate with an external shield approaching the envelope from the out- 0 side. I prefer to so arrange the cooperating parts. do that a portion of the periphery of the grid will run parallel to a portion of the shield for a distance not substantially less than the thickness of the glass, the parallel portions being separated by a not substantially greater distance than the thickness of the glass. I then position the anode on one side of the grid and the cathode at the other.

The broad aspects of my invention may be further understood by reference to the drawing.

Referring directly to the embodiment of my invention shown in Figures 1 and 2, a grid electrode I is preferably formed out of suitable material, of circular shape, and provided with a central aperture 2 crossed by grid wires 4. I prefer to extend the grid material along all radii to the walls of the envelope, and there provide a flange 5 running parallel with the envelope, this flange being preferably longer than the thickness of the envelope material at that point.

In one end of the envelope I provide a cathode 6, supported by cathode leads 1, and in the other end of the envelope I provide an anode 8, supported by an anode lead 9. These electrodes are positioned opposing each other so that electron flow from the cathode may pass through the grid wires and be collected by the anode on the other side.

An external shield I0 is preferably provided with an apertured plate ll having a shield lip I 2 formed thereon of an extent substantially equal to the lip 5 of the grid. The apertured plate is fastened to the shield by screws I4. I then prefer to position the tube within the apertured plate so that the lips 5 and I2 are abutting and separated only by the material of the envelope. In order to complete the shield, I pass a grid lead l through the wall of the envelope, preferably near the grid, and connect this both to the grid and to the apertured plate.

I may prefer to cement the apertured plate I I to the envelope of the tube and then utilize the plate as a means of mounting the tube on the shield.

Figure 3 shows another embodiment wherein the shield I0 is provided with an aperture I6, the apertured plate having been done away with. In this case I prefer to decrease the diameter of a portion of the envelope to form a shoulder H, the diameter of this shoulder above the shield l0 being larger than the aperture [6. I then extend the grid close to the shoulder to fill the entire diameter of the larger portion of the envelope so that when the tube is positioned in the aperture, the grid will overlap the shield and run parallel to it for a distance longer than the thickness of the glass between the shield and the grid. The grid is connected to the shield in a manner similar to that described for the embodiment shown in Figure 1.

The cooperation between the grid and the shield is such that, being separated substantially only by the thickness of the glass and being directly connected together, the shield becomes an effective continuation of the grid material and the shielding, for all practical purposes, is complete.

The combined shield, formed by the abutment of the grid with th external portion, is preferably used to separate a pair of tuned circuits, as shown in Figure 4. Here the grid electrode l is shown grounded and may be extended to completely surround one or both of the tuned circuits. An anode tuned circuit comprising the anode inductance I9 and anode variable capacity 20, is connected in series with an anode source 2| to the anode, the other end of the anode source going to a common anode-cathode point 22, grounded for radio frequency through condenser 23. The anode source is also preferably shunted by a by-pass capacity 24.

As the cathode I2 requires two leads for conducting current thereto, it is desirable to include both leads in a cathode-tuned circuit. This may be done in several ways, all well known in the art, but I prefer to make one lead a hollow conductor 25 wound into an inductance, the other lead 26 being run through the tube. The hollow conductor 25 and inner lead 26 are then connected to a cathode source 27, the ends of the hollow conductor being shunted by a cathode variable capacity 29 to complete the cathode-tuned circuit. The hollow conductor side of the cathode source is then connected to the common anode-cathode point 22.

'The circuit thus formed will cause the tube to oscillate, having parallel tuned-anode tunedcathode circuits, behaving in much the same manner as the well known tuned-grid tunedplate circuit, in which the coupling between the two circuits is the anode-grid capacity. In this case the coupling is the anode-cathode capacity.

The tube and circuit described, however, differ from the ordinary tuned-grid tuned-plate combination in that in this example the two fluctuating electrodes are separated by the grounded grid. The electron stream, however, is under complete control as the grid is in its usual position for proper control. Furthermore, as control is increased, as by making the grid wires finer and closer together, the shielding becomes better and reaches the pointwhere it is virtually complete.

The tube as above described, in combination with the related circuits, will oscillate freely and supply substantial amounts of power of high frequencies at which the usual tube and associated circuits fail.

I claim:

A thermionic tube adapted to cooperate with an external conductive shield having an aperture therein, comprising an envelope having a circular cross section dimensioned to fit said aperture, an anode in one end of said envelope, a cathode in the other end of said envelope, said anode and cathode being on opposite sides of said aperture, and a control electrode between said anode and cathode in the plane of said aperture, said control electrode extending to the inner wall of said envelope along all radii, and conductively connected to said shield through the wall of said envelope, the abutting edges of said control electrode and said aperture being separated by not substantially more than the thickness of the envelope wall and being parallel for a distance greater than said thickness.

RALPH M. HEINTZ. 

